The V2 uses an 11mm shaft instead of the 10mm that the V1, Trex 550 and Trex 600 use.

@Adventurer - you sure 'bout that ? I thought you can just exchange the V1 vs. the V2 head. I mean you do need a different shaft,since it needs to be shorter as I assume, but if the V2 shaft is +1mm in diameter, then you would also need a new swashplate, new bearings, new maingear, new belt-driver gear, etc. etc. to do the upgrade.

Well I have a V2 headed my way and will be able to measure some time next week.